1. Field of the Invention
The present invention relates to an optical network terminal (ONT) and, more particularly, to an ONT with low-power sleep logic that substantially extends the life of the battery after the AC main power supply has been lost.
2. Description of the Related Art
The subscriber end of a Fiber-To-The-Home (FTTH) network terminates a fiber optic cable in an optical network terminal (ONT) positioned at an interior or exterior location on a subscriber's premise. As a result, a substantial amount of bandwidth can be made available to the subscriber to provide a variety of services, such as plain old telephone service (POTS), Internet access (data) service, and video service.
One of the requirements of a POTS provider is to insure that, after the AC main power has failed, telephone service, known as lifeline telephone service, is continuously available for a period of time, such as eight hours. In an FTTH network, this is accomplished by providing a battery backup (BBU), such as an uninterruptible power supply, at the subscriber's premise. Thus, when power is lost, the BBU at the subscriber's premise provides power to the ONT at the subscriber's premise to maintain the lifeline telephone service for the required period of time.
FIG. 1 shows a block diagram that illustrates a prior-art FTTH network 100. As shown in FIG. 1, FTTH network 100 includes an optical line terminal (OLT) 102, a subscriber 104, a battery backup (BBU) 106, and an ONT 108 that is connected to OLT 102, subscriber 104, and BBU 106.
ONT 108 passes data signals and telephone signals between OLT 102 and subscriber 104, and transmits a video signal from OLT 102 to subscriber 104. For example, in the upstream pathway, ONT 108 receives a video signal, a data signal, and a voice signal from OLT 102; and transmits the video signal, the data signal, and the voice signal to subscriber 104 when power from an AC main power source is present. In this case, ONT 108 consumes a first amount of power when ONT 108 simultaneously transmits the video signal, the data signal, and the voice signal.
As further shown in FIG. 1, ONT 108 includes a microprocessor 110 that controls the operation of ONT 108 when the AC main power source has been lost. In addition to microprocessor 110, ONT 108 also includes a triplexer 112 (an optical transceiver that is connected to a fiber to carry an upstream wavelength, a down stream wavelength, and a video overlay wavelength) that is connected to a fiber optic cable. Further, ONT 108 includes a flash memory 114, a RAM memory 116, a clock driver 118, an I2C 120, a media access controller 122, and a voltage converter 124. These devices, along with microprocessor 110 and triplexer 112, constitute the core logic devices of ONT 108.
To provide telephone service, ONT 108 also includes a number of, such as four, subscriber line interface circuits (SLICs) 130, which each provide interfaces to the phone lines of the subscribers, and a subscriber line audio-processing circuit (SLAC) 132, which provides an interface between the SLICs 130 and triplexer 112. ONT 108 additionally includes a 10/100 physical layer circuit 134, a dual RS232 converter 136, a phase locked loop 140, and a number of LEDs 142.
Further, ONT 108 includes a power supply that includes a first power supply 150 that outputs first and second voltages, such as 3.3V and 5.0V, a second power supply 152 that outputs a third voltage, such as 12V, and a third power supply 154 that outputs fourth and fifth voltages, such as −30V and −90V. First, second, and third power supplies 150, 152, and 154 supply power from the AC main power supply when the AC main power supply is available, and from backup battery 106 when the AC main power supply is no longer available.
As shown, each of the above devices (except for the other power supplies), is connected to the first power supply 150 to receive the first voltage (3.3V). In addition, the triplexer 112 and a 12V external source 166 are connected to the second power supply 152 to receive the third voltage (12V). Further, the SLICs 130 are also connected to the first power supply 150 to receive the second voltage (5V). The SLICs 130 are additionally connected to the third power supply 154 to receive the fourth and fifth voltages (−30V and −90V).
In operation, microprocessor 110 continuously monitors an AC main power supply, and checks a battery power status indicator that is output from BBU 106. The battery status indicator can indicate, for example, whether the power supply or the battery module is providing the power, whether or not the battery in BBU 106 is charged or needs charging, and whether or not the battery in BBU 106 needs replacing.
When a loss of power from the AC main power source is detected, microprocessor 110 reports the lost power condition to OLT 102, and stops the transmission of the video signal. In addition, BBU 106 provides power (when the battery power status indicator indicates that BBU 106 is charged and has the power to provide). In this case, ONT 108 consumes a second amount of power when ONT 108 simultaneously transmits the data signal and the voice signal without the video signal. The second amount of power, in turn, is less than the first amount of power, thereby saving power.
Further, after the AC main power source has been lost for a predetermined period of time, microprocessor 110 stops the transmission of the data signal. In this case, ONT 100 consumes a third amount of power when ONT 108 only transmits the voice signal. The third amount of power, in turn, is less than the second amount of power, thereby saving additional power.
When the power provided by BBU 106 reaches a failure threshold (or when the power from the power supply reaches a failure threshold when BBU 106 has previously failed or is unavailable), microprocessor 110 detects this condition, known as a last gasp condition, and reports the condition to OLT 102.
During the last gasp condition, microprocessor 110 utilizes a charge stored in ONT 108 to allow microprocessor 110 to execute a controlled shut down. The charge, in turn, can be stored on a capacitor to provide a finite amount of energy. (ONT 108 can be implemented without a last gasp circuit.)
Once both power supplies have failed, ONT 108 shuts down, and does not turn on again until one of the two power supplies have returned. Throughout the time that power from the AC main power source is present, and during the time that power is supplied by BBU 106 (until the power from BBU 106 fails), microprocessor 110 detects off hook transitions that occur when subscriber 104 wishes to initiate a telephone call.
In the present example, ONT 108 provides lifeline support (detects off hook conditions while on battery power) for approximately eight hours. Although eight hours is a reasonable period of time, it is desirable to be able to provide lifeline support for a much longer period of time, such as twice as much or more.